In patients with chronic coronary artery disease and left ventricular dysfunction, it is important to determine the presence and extent of viable myocardium that may recover after revascularization. Both thallium uptake and the contractile response to dobutamine have been proposed to accurately assess myocardial viability in these patients. However, the relation between these two variables has not been established. To address this issue, 20 patients with coronary artery disease and chronic systolic dysfunction were studied. Of 312 myocardial regions assessed with transesophageal echocardiography, 203 (65%) had resting wall motion abnormalities. The proportion of myocardial segments with positive thallium uptake was significantly greater than the number of segments with a positive response to dobutamine. A relation between the two variables was found, such that the number of segments with a positive response to dobutamine was significantly greater among the myocardial regions with thallium uptake compared to those regions with no thallium uptake. The discordance between the two techniques was largely due to the presence of myocardial regions with thallium uptake but no response to dobutamine. Hence, in patients with coronary artery disease and chronic left ventricular dysfunction, a relation does exist between myocardial thallium uptake and the contractile response to dobutamine. However, the proportion of segments with thallium uptake is significantly greater than those with a positive response to dobutamine, indicating that inotropic reserve requires a higher degree of myocyte integrity than the preservation of membrane function.